1. Field of the Invention
The present invention relates to a method for forming a thin film and a film-forming device. More specifically, the present invention relates to a method for forming a thin film on a surface of a substrate by supplying a coating solution to the substrate such as a semiconductor wafer or a liquid crystal display (LCD) wafer, and further relates to a film-forming device used for the method.
2. Description of the Background Art
In the related art, technologies for manufacturing multilayer wiring boards have been employed in line with the development of highly integrated semiconductor devices. In a multilayer wiring structure, silicon oxide films, so-called spin-on-glass (SOG) films, are used as insulating films for insulating wiring, i.e., circuit patterns, from each other in the multilayer wiring boards.
The SOG films are generally formed by spin coating, namely, by applying a coating solution comprising a glass component dissolved in an organic solvent onto a substrate, and then calcining the coated solution by thermal treatment such as drying, baking, or curing to form a film.
A substrate surface has asperities due to circuit patterns formed on the substrate. Therefore, in known spin coating and thermal drying, a film is formed so as to trace the asperities and the film has unevenness in the surface shape. This disturbs later processes. For example, when lithography is carried out in a later process, deterioration in line width (CD) is caused by a difference in depth of focus. In addition, the unevenness of the surface increases with the number of laminated films. Thus, various problems arise.
Consequently, planarization of thin films is necessary. As a method for planarizing a thin film, a chemical mechanical polishing (CMP) method is known. The CMP method is conducted by hardening a thin film on a substrate by thermal treatment and then removing a part of the thin film by pressing a polishing member against the thin film. The polishing member is prepared by dropping a polishing solution containing mechanical polishing abrasive and chemical polishing abrasive to the surface of a polishing pad.
Another method (device) for planarizing a film is known (see, for example, Japanese Patent Laying-Open No. 07-047324). This method does not require a high-loaded process as in the CMP method. The method is conducted by supplying a coating solution to a substrate surface with asperities, thinly spreading the coating solution over the surface of the substrate by using a scanner plate to form a thin film, and, simultaneously, uniformly pressing the film by means of air pressure from a slit-shaped nozzle.
According to another method (device), a thin film is formed by supplying a coating solution onto the surface of a substrate and then supplying a gas containing solvent vapor to uniformly reduce the thickness of the film (for example, Japanese Patent Laying-Open No. 11-329938).
However, in the former method, namely, the technology disclosed in Japanese Patent Laying-Open No. 07-047324, since the air is blown toward the coating solution, the solution vaporizes to be hardened. Consequently, the fluidity of the coating solution is decreased causing insufficient uniformity of the thin film.
In the latter method, namely, the technology disclosed in Japanese Patent Laying-Open No. 11-329938, since the solvent vapor is supplied to the coating solution, the vaporization of the coating solution is avoided compared with the former method. However, the thin film is hardened by vaporization due to influence of the surrounding circumstances of a treatment place, as in the former method. Consequently, the fluidity is decreased. Thus, this method also cannot sufficiently achieve uniformity of the thin film.